CAPEC95

This attack targets the WSDL interface made available by a web service. The attacker may scan the WSDL interface to reveal sensitive information about invocation patterns, underlying technology implementations and associated vulnerabilities. This type of probing is carried out to perform more serious attacks (e.g. parameter tampering, malicious content injection, command injection, etc.). WSDL files provide detailed information about the services ports and bindings available to consumers. For instance, the attacker can submit special characters or malicious content to the Web service and can cause a denial of service condition or illegal access to database records. In addition, the attacker may try to guess other private methods by using the information provided in the WSDL files.

Attack Execution Flow

The first step is exploratory meaning the attacker scans for WSDL documents. The WDSL document written in XML is like a handbook on how to communicate with the web services provided by the target host. It provides an open view of the application (function details, purpose, functional break down, entry points, message types, etc.). This is very useful information for the attacker.

The second step that a attacker would undertake is to analyse the WSDL files and try to find potential weaknesses by sending messages matching the pattern described in the WSDL file. The attacker could run through all of the operations with different message request patterns until a breach is identified.

Once an attacker finds a potential weakness, they can craft malicious content to be sent to the system. For instance the attacker may try to submit special characters and observe how the system reacts to an invalid request. The message sent by the attacker may not be XML validated and cause unexpected behavior.

Attack Prerequisites

A client program connecting to a web service can read the WSDL to determine what functions are available on the server.

The target host exposes vulnerable functions within its WSDL interface.

Typical Likelihood of Exploit

Likelihood: High

Methods of Attack

Analysis

API Abuse

Examples-Instances

Description

A WSDL interface may expose a function vulnerable to SQL Injection.

Description

The Web Services Description Language (WSDL) allows a web service to advertise its capabilities by describing operations and parameters needed to access the service. As discussed in step 5 of this series, WSDL is often generated automatically, using utilities such as Java2WSDL, which takes a class or interface and builds a WSDL file in which interface methods are exposed as web services.

Because WSDL generation often is automated, enterprising hackers can use WSDL to gain insight into the both public and private services. For example, an organization converting legacy application functionality to a web services framework may inadvertently pass interfaces not intended for public consumption to a WSDL generation tool. The result will be SOAP interfaces that give access to private methods.

Another, more subtle WSDL attack occurs when an enterprising attacker uses naming conventions to guess the names of unpublished methods that may be available on the server. For example, a service that offers a stock quote and trading service may publish query methods such as requestStockQuote in its WSDL. However, similar unpublished methods may be available on the server but not listed in the WSDL, such as executeStockQuote. A persistent hacker with time and a library of words and phrases can cycle thru common naming conventions (get, set, update, modify, and so on) to discover unpublished application programming interfaces that open doors into private data and functionality.